How to resize digital images for printing

As the quality of digital cameras goes up, so does the volume of pixels they can capture. These days, shooting in your camera’s highest quality mode can yield an image bigger than your printer can actually print. While most image editing programs are happy to resize your photo for you in their respective print dialog boxes, knowing how to do it yourself gives you more control.

In this article, you’ll learn how to resize those big images from your digital camera for print using Adobe Photoshop and Photoshop Elements. Happily, the steps are exactly the same in either program.

Resolution and document size

To begin, you need two numbers: document (or rather, print) size and resolution. When printing one photo per page, your document size is most often the same as your paper size.

The next number refers to pixel size and, as discussed in our image resolution primer, resolution is the measurement that controls it. The goal in printing is to make the pixels too small to be seen individually (otherwise the print will look blocky). This involves increasing the resolution beyond that at which your camera was set (typically 72 or 150 ppi, depending on the model and manufacturer). If you’re printing on an inkjet printer at home, your resolution should fall somewhere between 240 and 480 ppi if you’re using glossy or matte paper, or 180 and 240 ppi for regular or textured paper.

Resizing with the Image Size dialog box

If your image doesn’t need to be cropped, you can use the Image Size dialog box for resizing. This dialog box is also handy for learning how big you can print your image at a given resolution. (For example, if you used a lower quality setting on your camera, your image may not contain enough pixels to print an 8-by-10-inch photo at high resolution.)

If you were to print this image, you’d need a piece of paper that’s over 40-by-30 inches! Luckily, by increasing resolution you can make the pixels smaller, which results in a smaller document size.

You can summon this dialog box in Adobe Photoshop (any version) by opening a photo and choosing Image -> Image Size (in Photoshop Elements, choose Image -> Resize -> Image Size, or press Command-Option-I in either program). The resulting dialog box reveals all kinds of information about your photo such as file size (how much space it takes up on your hard drive), pixel dimensions, and—most importantly for print—the Document Size section that tells you how big the photo would be if you printed it at its current resolution.

First, you need to lock your photo’s pixel dimensions by turning off the Resample Image checkbox at the bottom of the dialog box. This lets you experiment with document size and resolution without altering the number of pixels your photo contains (which preserves photo quality).

Next, enter your desired document size into the width field; both the height and resolution will change automatically to preserve the aspect ratio (the relationship between width and height). If the resulting resolution falls within the guidelines mentioned earlier, press OK and your photo will be resized accordingly. If the resolution is too low, enter a smaller document size. Alternatively, you can enter the desired resolution and Photoshop will recalculate the document size for you.

Resizing with the Crop Tool

If your photo needs cropping—or if you can’t get exactly the right dimensions by using the Image Size dialog box—you can use the Crop tool and dial the width, height, and resolution right into the Options bar.

By entering 7 inches into the width field, the height automatically changes to preserve the photo’s aspect ratio. As you can see, there are enough pixels and resolution to print a high-quality 5-by-7 photo.

In either Photoshop or Photoshop Elements, open your photo and press C on your keyboard to activate the Crop tool. Trot up to the Options bar at the top of your screen and enter “10 in” for width and “8 in” for height (you must include the unit of measurement, though you don’t have to use quotations marks). In the resolution field, enter 240.

If your cropped image is enlarged, you’ve entered too large of a physical size and/or too high of a resolution for the number of pixels your image contains. Undo and try again.

Tip: If you want to crop a photo while preserving its original aspect ratio, draw a crop box around the whole photo and then hold down the Shift key as you drag any corner handle diagonally inward. You can also use the arrow keys on your keyboard to nudge the crop box into place.

When you’ve got the crop box just right, press Return or double-click within the box to accept it. If your image appears to enlarge once you accept the crop, you’ve entered too large of a physical size and/or too high of a resolution for the number of pixels your image contains. In that case, press Command-Z to undo the crop and enter either a smaller print size or lower resolution, or both.

Mouse over to your image and click and drag diagonally to draw a crop box. You can click and drag within the box to move it atop your photo, or drag any corner handle to adjust the box size.

[Lesa Snider, author of Photoshop CS5: The Missing Manual (Pogue Press/O’Reilly) and co-author of the upcoming iPhoto 11: The Missing Manual (Pogue Press/O'Reilly), records training videos for KelbyTraining.com and Lynda.com, is chief evangelist of iStockphoto.com, a long-time member of the Photoshop World Instructor Dream Team, and founder of GraphicReporter.com .]